As conventional methods for detecting surface unevenness (asperity) of an object under inspection by image processing, there are the light-section method for measuring surface shape and the image-based determination method using a color camera (refer to Patent Documents 1 to 3, for example).
The light-section method goes as follows: For example, as a tire is rotated, a slit light is cast at a surface of the tire by an illuminating means capable of casting monochromatic light such as a semiconductor laser, and the portion illuminated by the slit light is shot by an area camera. Then after the two-dimensional coordinates of the shot slit image are obtained, the outer shape of the tire is derived by converting the two-dimensional coordinates into three-dimensional coordinates using the angle of rotation of the tire. Thus, by comparing this outer shape against reference images stored in advance, tire shapes in the bead region, the tread region, the sidewall region, and the like can be inspected.
On the other hand, in the proposed image-based determination method using a color camera, a white slit light is cast at the surface of an object under inspection, and the reflected image is shot by a line camera. And from the shot color image, surface unevenness (indentations and bumps), state of undulation, or subtle changes in color of the surface of the object under inspection are detected. Note, however, that it is not necessary that the line camera be a color camera. And a grayscale image of the object under inspection may be shot using a monochromatic light as the slit light, and surface unevenness, state of undulation, or subtle changes in color may be detected from the shades of the shot image.